Method for making ferroelectric thin-film, sensor and the ferroelectric thin-film element

Abstract

A ferroelectric thin-film element has a Si substrate and a thin-film laminate formed on the Si substrate, the thin-film laminate being a buffer layer epitaxially grown on the Si substrate, a metallic thin film lower electrode epitaxially grown on the buffer layer, a ferroelectric thin film orientationally grown or epitaxially grown on the lower electrode, and an upper electrode formed on the ferroelectric thin film. A portion of the thin-film laminate may be supported by air.

What is claimed is:  
     
       1. A method for making a ferroelectric thin-film element comprising an Si substrate and a thin-film laminate formed on the Si substrate, a portion of the thin-film laminate being disposed so as to be unsupported, the method comprising the steps of: 
       epitaxially growing a buffer layer on the Si substrate;  
       forming a lower electrode by epitaxially growing a metallic thin film on the buffer layer;  
       orientationally growing or epitaxially growing a ferroelectric thin film on the lower electrode;  
       forming an upper electrode on the ferroelectric thin film; and  
       removing a portion of the buffer layer to form a recess in the buffer layer such that a part of the thin-film laminate is unsupported, wherein said recess does not extend to a bottom surface of the ferroelectric thin-film.  
     
     
       2. A method for making a ferroelectric thin-film element according to  claim 1 , wherein the removing step comprises etching a portion of the buffer layer. 
     
     
       3. A method for making a ferroelectric thin-film element according to  claim 1 , wherein the step removing comprises etching a portion of the buffer layer without etching the Si substrate. 
     
     
       4. A method for making a ferroelectric thin-film element according to  claim 3 , further comprising etching at least a portion of the buffer layer located adjacent the recess or through-hole of the Si substrate. 
     
     
       5. A method for making a ferroelectric thin-film element according to  claim 1 , wherein the buffer layer comprises at least one member selected from the group consisting of an MgO layer, a Ti 1-x Al x N layer where x is 0 to about 0.4 and a YSZ layer. 
     
     
       6. A method for making a ferroelectric thin-film element according to  claim 5 , wherein the lower electrode comprises a material selected from the group consisting of Ir, Rh, Pt, SrRuO 3  and (La, Sr)CoO 3 , and wherein the ferroelectric thin film comprises a perovskite compound represented by the general formula ABO 3  where A is at least one of Ba, Pb and La, and B is at least one of Ti, Zr, Mg, Nb and Zn. 
     
     
       7. A method for making a ferroelectric thin-film element according to  claim 1 , wherein the lower electrode comprises a material selected from the group consisting of Ir, Rh, Pt, SrRuO 3  and (La, Sr)CoO 3 . 
     
     
       8. A method for making a ferroelectric thin-film element according to  claim 1 , wherein the ferroelectric thin film comprises a perovskite compound represented by the general formula ABO 3  where A is at least one of Ba, Pb and La, and B is at least one of Ti, Zr, Mg, Nb and Zn. 
     
     
       9. A method for making a ferroelectric thin-film element comprising an Si substrate and a thin-film laminate formed on the Si substrate, a portion of the thin-film laminate being disposed so as to be unsupported, the method comprising the steps of: 
       epitaxially growing a buffer layer on the Si substrate;  
       forming a lower electrode by epitaxially growing a metallic thin film on the buffer layer;  
       orientationally growing or epitaxially growing a ferroelectric thin film on the lower electrode;  
       forming an upper electrode on the ferroelectric thin film; and  
       removing a portion of the Si substrate and the buffer layer to form a recess in the Si substrate such that a part of the thin-film laminate is unsupported, wherein said recess does not extend to a bottom surface of the ferroelectric thin-film.